The present invention broadly relates to a new and improved method of marking substantially flat or superficial paper articles, especially folded or multi-page printed products. The present invention also relates to a new and improved method of producing a collated paper end product and monitoring the completeness of such collated paper end product which is composed of different types of such paper articles.
It is well known to mark paper articles using luminophores. Luminophore markings are used because such markings are practically transparent as well as invisible to the human eye when illuminated with light of the visible spectrum. Therefore, such markings do not impair graphical characters or symbols imprinted on the paper article. Luminophore markings, however, are discernible or recognizable by means of specific luminescence scanners, provided these markings are illuminated with a special light, in particular light from the ultraviolet region of the spectrum. Another advantage of using luminescence scanners is that such luminescence scanners, when utilizing proper illumination, can be precisely adjusted to the wavelength of the back-scattered radiation from the luminophore and therefore remains widely unaffected by other light.
Known luminophore markings are applied, for instance, to the flat side of paper material possessing a certain value or property characteristic, such as for providing a security or anti-falsification marking for, for instance, papers used to print checks or other negotiable instruments as well as postage stamps. It is also known in appropriate instances to apply these luminophore markings to one flat side of a paper article in a pattern representing a code. However, evaluation of the luminophore markings which are applied to the flat side in a conventional manner, requires that such flat side is laid bare. A reliable evaluation of the known luminophore markings is not possible when the flat side of the paper article bearing the marking is only partially covered, for example, by a paper article of a similar type. It is for this reason that the use of luminophore markings has been restricted hitherto to relatively few fields of application.